Merge branch 'isdn-hisax-Fix-pnp_irq-error-checking'

Arvind Yadav says:

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isdn: hisax: Fix pnp_irq's error checking

The pnp_irq() function returns -1 if an error occurs.
pnp_irq() error checking for zero is not correct.
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Signed-off-by: David S. Miller <davem@davemloft.net>